A gas turbine engine may be used to power various types of vehicles and systems. A particular type of gas turbine engine that may be used to power aircraft is a turbofan gas turbine engine. A turbofan gas turbine engine may include, for example, five major sections: a fan section, a compressor section, a combustor section, a turbine section, and an exhaust section.
During operation, a fan induces air from the surrounding environment into an inlet of the fan section and accelerates a fraction of this air toward the compressor section. The compressor section raises the pressure of the air it receives from the fan section to a relatively high level. The pressurized air enters the combustor section, where a ring of fuel nozzles injects a steady stream of fuel into a plenum formed by liner walls and a dome. The injected fuel is ignited in the combustor, which significantly increases the energy of the compressed air. The high-energy compressed air from the combustor section then flows into and through the turbine section, causing rotationally mounted turbine blades to rotate and generate energy. The air exiting the turbine section is exhausted from the engine via the exhaust section, and the energy remaining in the exhaust air aids the thrust generated by the air flowing through the bypass plenum.
Generally, the rotating components of the engine are supported by bearings. In cooler sections of the engine, such as the fan section, one or more foil bearings may be included. A foil bearing generally includes a journal (mounted to the rotating component) and a cylindrical top foil disposed therearound. The journal and top foil are in contact when stationary and at low journal rotational speeds. They are spaced apart from each other during high rotational speed. The journal is typically coated with a hard, organic material to thereby prevent premature wear. Cool air may also be provided between the journal and top foil.
Although foil bearings have advantages, they have some drawbacks. For example, foil bearings may not be useful in high temperature applications, such as in the compressor or combustor sections of the gas turbine engines. Specifically, the material used for the journal coating may vaporize when exposed to high temperatures, such as 315° C. and above. To prevent coating vaporization, the foil bearing is preferably cooled to an acceptable temperature. However, cooling down the foil bearing from the high temperatures presents certain challenges. In particular, liquid-cooling the foil bearing may not be practical, because potential cooling liquids may vaporize when exposed to the high temperatures. Moreover, a large amount of air may be needed to air-cool the foil bearing, thereby undesirably decreasing engine efficiency.
Hence, there is a need for a foil bearing system that may be implemented into high temperature sections of the gas turbine engine, such as in the compressor or combustor sections. It is also desirable for the system to be lightweight and capable of being retrofitted into existing gas turbine engines. Moreover, it is desirable to have methods for manufacturing the system that are cost-effective.